Electrophysiological Properties of the Canine Ventricular Fiber

A certain electrophysiological features of the ventricular fiber have been investigated in the papillary muscle of the dog by the use of a special method for polarizing, extracellularly and simultaneously, a large number of its fibers.1) The electrotonic potential and its spatial decay was found to conform with the cable law as if it were in a single fiber. The space and time constants of the ventricular fiber could be estimated from the slopes of lines denoting interrelationships between the amplitude and the half time of rise of electrotonic potential to distance respectively. The calculated space constant was 1.3 mm, and the time constant was 2.0 msec.2) The critical membrane potential was -65 mV.3) The membrane resistance was found to decrease slightly at the peak of spike (to not less than 90% of resting resistance), and to remain about the same during the entire phase of plateau in the resting phase.4) The action potential in the ventricular fiber could be abolished by anodal current even in the early stage of repolarization. The effectiveness of anodal polarization varied depending on the duration of current pulse and the timing of application: the longer the duration and later its application, the higher was the efficiency for producing the abolition.5) In general, there seems to be no essential difference in nature of membrane between the ventricular and Purkinje fibers. The observed differences in electrophysiological behaviors between the two appear to be dependent rather on the difference in their fiber architectonic.